1. Field of the Invention
The present invention relates to a contact type image sensor and, more particularly, to a contact type image sensor having a frame body to hold a light source to irradiate light onto an original, photoelectric converting elements for photoelectrically converting the light from the original, and an image pickup device for guiding the light from the original to an array of the photoelectric converting elements.
2. Related Background Art
Hitherto, as shown in a cross-sectional view in FIG. 7, a contact type image sensor has been constructed in a manner such that the sensor array 8 corresponding to a length of an original to be read, a point light source array 1 in which a plurality of point light sources 2 for irradiating the original surface are arranged in a line on a board, an image pickup device array 7 to form an image of the light from the original onto a light receiving portion of photoelectric converting elements 9 on the sensor array 8, and a cover glass 11 to support the original are positioned and fixed to one frame body 10.
As a point light source array 1, LED elements are generally used, with a view to low electric power consumption and a long life. The LED elements are attached in a line on a board made of a material such as glass epoxy or the like together with resisters for current limitation by soldering or the like.
However, in the above conventional contact type image sensor, there are the following problems.
(1) That is, in the above conventional sensor, since the cover glass 11 and the frame body 10 are separate and individual parts, they increase costs, because of the number of parts and because of a process for adhering the cover glass 11 to the frame body 10 in order to position and fix the cover glass is needed and the like.
(2) It is difficult to completely eliminate a height difference between the cover glass 11 and the framing body 10, in terms of precision. Therefore, in the case of a reading apparatus of a sheet-through type, in order to prevent the original colliding with the portion of different height portion, it is necessary to take a countermeasure such that a Mylar.RTM. sheet is adhered to the portion of height different or the like, so that it also causes an increase in costs.
(3) There is also a technical point to be noted. A solder ball formed at the time when the LED elements of the LED array are soldered, or foreign matter such as a board scrap from an LED board cut surface or the like, adhered to the light source is moved into the optical path of a rear surface of the cover glass 11, thereby shielding or reflecting the light from the light source 2 onto an original reading line or the light from the original reading line to the image pickup device, so that erroneous information is picked up by the sensor and appears as a black stripe or a white stripe in an output image.